On 11/24/20 15:50, Will Deacon wrote: > When confronted with a mixture of CPUs, some of which support 32-bit Confronted made me laugh, well chosen word! :D For some reason made me think of this :p https://www.youtube.com/watch?v=NJbXPzSPzxc&t=1m33s > applications and others which don't, we quite sensibly treat the system > as 64-bit only for userspace and prevent execve() of 32-bit binaries. > > Unfortunately, some crazy folks have decided to build systems like this > with the intention of running 32-bit applications, so relax our > sanitisation logic to continue to advertise 32-bit support to userspace > on these systems and track the real 32-bit capable cores in a cpumask > instead. For now, the default behaviour remains but will be tied to > a command-line option in a later patch. > > Signed-off-by: Will Deacon <will@xxxxxxxxxx> > --- > arch/arm64/include/asm/cpucaps.h | 2 +- > arch/arm64/include/asm/cpufeature.h | 8 ++- > arch/arm64/kernel/cpufeature.c | 106 ++++++++++++++++++++++++++-- > 3 files changed, 107 insertions(+), 9 deletions(-) > > diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h > index e7d98997c09c..e6f0eb4643a0 100644 > --- a/arch/arm64/include/asm/cpucaps.h > +++ b/arch/arm64/include/asm/cpucaps.h > @@ -20,7 +20,7 @@ > #define ARM64_ALT_PAN_NOT_UAO 10 > #define ARM64_HAS_VIRT_HOST_EXTN 11 > #define ARM64_WORKAROUND_CAVIUM_27456 12 > -#define ARM64_HAS_32BIT_EL0 13 > +#define ARM64_HAS_32BIT_EL0_DO_NOT_USE 13 nit: would UNUSED be better here? Worth adding a comment as to why too? > #define ARM64_HARDEN_EL2_VECTORS 14 > #define ARM64_HAS_CNP 15 > #define ARM64_HAS_NO_FPSIMD 16 [...] > +static bool has_32bit_el0(const struct arm64_cpu_capabilities *entry, int scope) > +{ > + if (!has_cpuid_feature(entry, scope)) > + return allow_mismatched_32bit_el0; If a user passes the command line by mistake on a 64bit only system, this will return true. I'll be honest, I'm not entirely sure what the impact is. I get lost in the features maze. It is nicely encapsulated, but hard to navigate for the none initiated :-) Thanks -- Qais Yousef > + > + if (scope == SCOPE_SYSTEM) > + pr_info("detected: 32-bit EL0 Support\n"); > + > + return true; > +} > + > static bool has_useable_gicv3_cpuif(const struct arm64_cpu_capabilities *entry, int scope) > { > bool has_sre; > @@ -1803,10 +1890,9 @@ static const struct arm64_cpu_capabilities arm64_features[] = { > }, > #endif /* CONFIG_ARM64_VHE */ > { > - .desc = "32-bit EL0 Support", > - .capability = ARM64_HAS_32BIT_EL0, > + .capability = ARM64_HAS_32BIT_EL0_DO_NOT_USE, > .type = ARM64_CPUCAP_SYSTEM_FEATURE, > - .matches = has_cpuid_feature, > + .matches = has_32bit_el0, > .sys_reg = SYS_ID_AA64PFR0_EL1, > .sign = FTR_UNSIGNED, > .field_pos = ID_AA64PFR0_EL0_SHIFT, > @@ -2299,7 +2385,7 @@ static const struct arm64_cpu_capabilities compat_elf_hwcaps[] = { > {}, > };
